How Do Jet Engines Actually Work?

October 03, 2025

How Do Jet Engines Actually Work?

By Ayush Rao

“It might be assumed that the flying machine which will really fly might be evolved by the combined and continuous efforts of mathematicians and mechanicians in from one million to ten million years”.

In a 1903 New York Times article, this was once speciously stated with such falsifying conviction that mankind would not fly for a million years yet a shocking 2 months and 8 days later, the Wright Brothers had that canonical, ceremonial flight that changed the course of mankind and its endeavours completely . Engines are what we owe this revolutionary power of flight to.

Every time you board a flight, you're trusting your life to a metal machine strapped on to the wings of a hollow tube that swallows air, compresses it, ignites it, and shoots it out the back at enormous speed. It sounds terrifying when you put it that way. But the jet engine is one of the most mechanically elegant pieces of engineering ever devised and once you understand how it works, it's hard not to find it beautiful.

The Core Idea: Newton's Third Law

At its heart, a jet engine is a machine for applying Newton's Third Law: for every action, there is an equal and opposite reaction. The engine pushes air backward and the reaction to that push is what drives the aircraft forward. This is the same principle that makes a deflating balloon fly across the room, scaled up to move a 400-tonne aircraft across continents.

The key challenge is doing this efficiently, powerfully, and reliably at temperatures and pressures that would destroy almost any ordinary material.

The Four Stages: Suck, Squeeze, Bang, Blow

Engineers sometimes summarize the jet engine's working cycle as 'suck, squeeze, bang, blow' and this is actually a decent shorthand for the four stages although seemingly irreverent to most.

First, intake. A large fan at the front of the engine sucks in enormous quantities of air. On a modern turbofan engine, the type used in most commercial aircraft, this fan alone does a huge amount of work, pushing air both into the core of the engine and around it. The air moving around the core (called bypass air) actually produces the majority of the thrust on modern engines, while also making the engine quieter and more fuel-efficient. Such engines are termed as high-bypass engines.

The General Electric GE9X, one of the most powerful commercial high-bypass jet engines ever produced.

Second, compression. The air entering the core passes through a series of compressor stages, spinning discs with carefully angled blades that progressively squeeze the air to a much higher pressure. By the time air reaches the combustion chamber, it may be compressed to 40 or 50 times atmospheric pressure and heated significantly just from being squeezed. Think of how a bicycle pump gets warm when you use it, same principle, dramatically amplified.

Third, combustion. Fuel, typically a bespoke kerosene-based jet fuel which is injected into the high-pressure air and ignited. The temperatures here are extraordinary: combustion gases can exceed 1,700 degrees Celsius, which is hot enough to melt the turbine blades made from nickel superalloys that sit just downstream. Engineers solve this by cooling the blades with air bled from the compressor, threading tiny channels through the blades and even coating them with ceramic thermal barrier coatings.

Fourth, exhaust. The superheated, high-pressure gases expand rapidly and are forced through the turbine. The turbine blades extract energy from the rushing gases and this extracted energy is used to spin the compressor and the front fan, which is connected by a shaft. The remaining energy in the exhaust gases produces the thrust that moves the aircraft forward.

The internal working of an engine

The Turbine Blade Problem

The turbine blade is one of the most remarkable objects in modern manufacturing. It must withstand temperatures thousands of degrees celsius above its own melting point , endure centrifugal forces tens of thousands of times stronger than gravity, and maintain its precise aerodynamic shape under these conditions, all while spinning thousands of times per minute. Single-crystal turbine blades, grown as a single grain of metal to avoid the weak boundaries between grains, are a genuine marvel of materials science.

Different Types of Jet Engines

The turbofan engine used in commercial aviation is the most common type today, optimized for efficiency at high altitudes and subsonic speeds. Military fighter jets often use turbojets or afterburning turbofans, which can inject additional fuel into the exhaust to produce massive bursts of thrust at the cost of very high fuel consumption. Turboprop engines, common on smaller commuter aircraft, use a jet engine to spin a propeller. And turboshaft engines, a variation of the same concept, power most helicopters.

Why It Matters

The jet engine shrank the world. A journey from Mumbai to London that once took weeks by ship now takes about nine hours. The reliability of modern jet engines is extraordinary. Commercial aviation has a safety record that makes it, mile for mile, the safest form of transport ever invented. The next time you hear that distinctive rising whine as the engines spool up on the runway, take a moment to appreciate what's happening: one of the most sophisticated machines humanity has ever built, turning fuel and air into the miracle of flight.

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